Passive porocess which relies on inbuilt motion (kinetic energy). It is simliar to diffusion in that it occurs down a concentration gradient. It is helped by a carrrier protein.
Particles are taken in one side of teh carrier protein in the cell-surface membrane, this causes a shape change and they are then released on the other side of the membrane.
the passage of water from a region which has a higher water potential to a region where it has a lower water potential through a partially premeable membrane.
the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of a higher concentration using energy and carrier molecules
Metabolic energy in the form of ATP is needed.
Materials move against a concentarion gradient. EG/ lower ---> higher
By using ATP directly to move molecules
By using a concentartion gradient that has already been set up by dircet transport, aka co-transport.
Absorption in the small intestine
Villi & microvilli,
glucose absorbed through the walls of the small intestine which contain villi, which increase the surface area for diffuse, the surface area is increased further by the villi containing microvilli.
They are thin walled, reducing teh distance over which diffusion take place.
Able to move & so help mantain a diffusion gradient.
Well supplied with blood vessels so that blood can carry away absorbed molecules.